Environmental Engineering Reference
In-Depth Information
8.11.2 surface foam and scum
The type, color, and amount of foam or scum present may indicate
the required wasting strategy to be employed. Types of foam include the
following:
•
fresh, crisp, white foam
—Moderate amounts of crisp white foam
are usually associated with activated sludge processes produc-
ing an excellent final effluent (normal operation; no adjustment
necessary).
•
Thick, greasy, dark tan foam
—A thick, greasy dark tan or brown
foam or scum normally indicates an old sludge that is overoxidized,
a high mixed liquor concentration, and too high of a waste rate (old
sludge; more wasting required).
•
White billowing foam
—Large amounts of a white, soap-suds-like
foam indicate a very young, underoxidized sludge (young sludge;
less wasting required).
8.11.3 sludge Color and odor
Though not as reliable an indicator of process operations as foam,
sludge color and odor are also useful indicators. Colors and odors that
are important include the following:
•
Chocolate brown/earthy odor
indicates normal operation (no adjust-
ment necessary).
•
light tan or brown/no odor
indicates sand and clay from infiltra-
tion/inflow (extremely young sludge; decrease wasting).
•
dark brown/earthy odor
indicates old sludge with high solids
(increase wasting).
•
Black color/
rotten egg odor
indicates septic conditions, low dis-
solved oxygen concentration, and too low of an airflow rate (increase
aeration).
8.11.4 Mixed liquor Color
A light chocolate brown mixed liquor color indicates a well-operated
activated sludge process.
8.12 final seTTling TanK (Clarifier) observaTions
Settling tank observations include flow pattern (normally uni-
form distribution), settling, amount and type of solids leaving with the
process effluent (normally very low), and the clarity or turbidity of the
process effluent (normally very clear). Observations should include the
following conditions:
